1. Field of the Invention
The present invention relates to an information record medium such as an optical disk of a high recording density type, which is capable of recording information such as video information, audio information and the like at a high density, and which is represented by a DVD (Digital Video or Versatile Disk). The present invention also relates to a recording-apparatus for recording the information onto the information record medium, and a reproducing apparatus for reproducing the information from the information record medium.
2. Description of the Related Art
Conventionally, a so-called LD (Laser Disk) and a so-called CD (Compact Disk) are generalized as optical disks, on which information such as video information, audio information and the like is recorded.
On the LD or the like, the video information and the audio information are recorded together with time information indicating time to reproduce each information with respect to a reproduction start position provided in each of the LD and the like as a standard. Therefore, the reproducing apparatus can easily perform a so-called "time search (or time-based search)" to search a recording position on the disk corresponding to an arbitrary time designated or specified by the audience, with reference to this time information. Further, other than a normal reproduction of the recorded data to reproduce the recorded information in the order of recording, special reproductions such as a reproduction in which the audience can select and listen to only desirable music among the musics recorded on the CD, a reproduction in which the audience can listen to the musics in a random reproducing order and so on, are possible on the basis of this time information.
However, there is such a problem in the above mentioned LD, CD and the like that an interactive and variegated reproduction is not possible in which the audience has several options as for the video image to be displayed or the audio sound to be reproduced, and the audience can listen to desirable one by selecting them.
More particularly, the above mentioned LD, CD or the like is not capable of interactive reproduction to output different types of video images or audio sounds depending on the contents of the "answer" inputted by the audience in response to a "question". Such interactive reproduction is often seen in recent game or educational software used in a personal computer. For example, if the answer is correct, an video image and an audio sound corresponding to the right answer are reproduced, and if the answer is incorrect, a video image and an audio sound corresponding to the incorrect answer are reproduced.
Meanwhile, various proposals and developments are being made as for the interactive reproduction of the DVD, which is an optical disk having an increased memory capacity ten times as much as that of the conventional CD without changing the size of the optical disk itself. In case of recording information onto this DVD, it is preferable to compress the video data etc. during recording, in order to use the memory capacity efficiently and increase the amount of information stored in the disk. Regarding the data compression technique utilized here, the image data compression technique called as the MPEG (Moving Picture Expert Group) 2 method, which is capable of changing the compression rate in correspondence with the contents of video data, is outstanding from view points of its high compression efficiency and its high reproducibility.
However, according to the research by the present inventors, it was found that, if data is compressed and recorded on the record medium, such as the DVD or the like, with variable compression rate by use of the MPEG 2 method, the relationship between the time and the recording position is lost (i.e., it is unknown which information is recorded at which recording position, and is corresponding to what time). Accordingly, it is expected that it becomes difficult for the reproducing apparatus to move the optical pickup to the appropriate recording position corresponding to designated time for the time search. Actuality is such that this problem itself, i.e., the difficulty in the time search with respect to the DVD containing the compressed data with variable compression rate, is not even recognized by those skilled in the art.
The present inventors paid attention to this difficulty, which has not been known to the public yet, in an earlier stage than others, and proposed the following methods in Japanese Patent Application No. Hei. 7-170913 (not laid open yet):
(I) a method for conducting the time search, wherein first address information indicative of the start address of pre-compressed primary data (e.g., video data) of every predetermined time unit (e.g., every 10 seconds) is recorded at a portion of the record medium different from the primary data recorded area, and the time search is conducted by the time unit with reference to the first address information; PA1 (II) a method for conducting time search, wherein second address information indicative of the start address of compressed data of every compressed time unit (e.g., every data for 0.5 seconds), in addition to the above mentioned first address information, is recorded at a portion of the record medium different from the primary data recorded area, and the time search is initially conducted roughly by the time unit with reference to the first address information, and is further conducted, from the roughly searched position, finely by the compression time unit with reference to the second address information; and PA1 (III) a method for conducting time search, wherein the above mentioned second address information and the number of the data frames (data unit composed of primary data of a certain time period) constituting the compression unit indicated by the second address are recorded at a portion of the record medium different from the primary data recorded area, without recording the above mentioned first address information, and the number of the data frames is counted and summed up to convert the number of the data frames to the time period, so that the time search is conducted in accordance with the converted time period.
In the above mentioned method (I), the search by every time unit is performed quickly by using a simple algorithm. However, in case of designating the time more minute than the time unit, the audience must just wait for the time normally elapsed while actually reproducing the information. If the time unit itself is shortened, this waiting time could be reduced on the whole. However, supposing that four bytes is required to indicate each address by the time unit of 1 second, the 120 minutes source requires: EQU (120[min].times.60[sec])/1[sec].times.4[bytes]=28800[bytes].
Thus, in order to realize the time search of the above mentioned method (I), the reproducing apparatus must have a memory of 28800 bytes.
According to the above mentioned method (II), after the rough search is initially conducted by the time unit of the method (I), the fine search is repeatedly conducted from the roughly searched position by the compressed unit. Thus, the fine time search is possible. However, assuming that the rough time unit is set to 10 seconds and the compressed unit is set to the data for 0.5 seconds, if four bytes are required to indicate each data, the 120 minute source requires: ##EQU1##
Thus, in order to realize the time search of the above mentioned method (II), the reproducing apparatus must have a memory of 60480 bytes.
The above mentioned method (III) allows quick search to the extent of the compressed unit. However, assuming that the compressed unit is set to the data for 0.5 seconds, if four bytes are required to indicate each address and one byte is required to indicate the number of the data frames, the 120 minute source requires: EQU (120[min].times.60[sec])/0.5[sec].times.(4[bytes]+1[byte])=72000[bytes].
Thus, in order to realize the time search of the above mentioned method (III), the reproducing apparatus must have a memory of 72000 bytes.
In this manner, according to the methods proposed by the applicant in Japanese Patent Application No. Hei. 7-170913, if the fine time search is conducted, the load on the hardware such as the necessary memory capacity of the reproducing apparatus would be fairly large.